Arc welding

ABSTRACT

Process for the arc welding of mild steel workpieces without external shielding of the arc by the use of cored tubular electrodes which deposit weld metal of improved physical properties and containing 0.5-1.3 percent aluminum 0.3-2 percent manganese, 0.1-1 percent silicon, not more than 0.12 percent carbon, and not more than 0.2 percent titanium, the balance substantially iron.

United States Patent [72] Inventors Paul Desmond Blake BishopsStortiord; Roy Douglas Johnston, Braughing Ware; Brian Phelps, Roydonnear Harlow; Edwin Albert Chapman, Cuftley, Potters Bar; Ronald LeonardBartlett, Cheshunt, England [21] Appl. No. 661,637

Filed Aug. 18, 1967 [54] ARC WELDING 6 Claims, 3 Drawing Figs.-

[52] U.S.Cl

51 1111. c1 15231135/22 50 FieldoiSearch 219/146; 117/205, 207; 148/24,26

[56] RefefencBS Cited UNITED STATES PATENTS 3,177,340 4/1965 061111161219/146 2,520,806 11/1949 Kihlgren 117/205 Primary Examiner-J. V. TruheAssistant Examiner-Lawrence A. Rouse Attorney-Cushman, Darby & CushmanABSTRACT: Process for the arc welding of mild steel workpieces withoutexternal shielding of the are by the use of cored tubular electrodeswhich deposit weld metal of improved physical properties and containing0.5-1 .3 percent aluminum 0.3-2 percent manganese, 0.1-] percentsilicon, not more than 0.12 percent carbon, and not more than 0.2percent titanium, the balance substantially iron.

PATENTEU'APR BIB?! 3573, 126

0 2 4 6 a 10 12 14 16 20 Y awe/ct 129 .2

awe/e6 0605(6) PAUL DESMgN D B Z KE 12 ROY DOUGLAS JOHNSTON BRIAN PHELPSEDWIN ALBERT CHAPMAN RONALD LEONARD BARTLETT 1 ARC WELDING lt has longbeen the practice to use for automatic and semiautomatic arc weldingcontinuous electrodes which are devoid of an external flux coating inconjunction with a sub merged arc flux or a shielding gas and in recentyears widespread use has been made of carbon dioxide as the shieldmggas.

An important function of the submerged arc flux and of the shielding gashas been to deny access to the weld metal of atmospheric oxygen andnitrogen. The use of a submerged arc flux, however, prevents observationof the weld metal by the operator, while the use of a shielding gas iscostly and requires cumbersome equipment. It has been proposed to avoidthe necessity for external shielding of the weld metal by the use of atubular electrode, consisting of a mild steel sheath having no externalflux coating but having a core containing deoxidizing elements, forexample manganese, aluminum and silicon, and also elements, such asaluminum, which are capable of com bining with nitrogen to formnitrides. Tubular electrodes of this kind as hitherto proposed have not,however, been capable of producing sound weld metal having the highductility and good impact strength characteristic of the mild steel weldmetal produced by good quality automatic electrodes used with ashielding medium.

The invention, in its broadest aspect, is based upon our discovery thatsound weld metal appropriate for welding mild steel workpieces andhaving such satisfactory physical properties can be produced by the useof a bare mild steel tubular arc welding electrode, containingdeoxidizers and nitrogen-fixing elements in its core, without shieldingof the are by gas or a submerged arc flux provided that the electrode isso formulated and the arc is drawn under conditions such that thecontents of carbon, aluminum, manganese, silicon and titanium in theweld metal are maintained within definite prescribed limits indicatedbelow.

The invention provides a process of automatic or semiautomatic weldingwhich consists in depositing from a cored tubular electrode, having amild steel sheath devoid of external flux, without external shielding ofthe arc weld metal having an elongation of at least 18 percent, areduction of area of at least 25 percent and a Charpy impact strength ofat least 35 ft/lbs. at 20 C and at least 20 ft/lbs. at -30 C when testedin accordance with the mechanical test procedure given in 8.5.8. 639,1964, the weld metal being of the following composition by weight:

aluminium-0.05- l .3 percent manganese0.3-2 percent silicon0.ll percentcarbon-0.12 percent max.

titanium-0.12 percent max. if the silicon content exceeds 0.35 percentand 0.25 percent max. if the silicon content is 0.35 percent or lessbalance-iron apart from incidental impurities.

The incidental impurities include sulfur and phosphorus and may includezirconium in an amount not exceeding 0.05 percent by weight.

Preferably the weld metal contains 0.120.8 percent aluminum, 0.71.75percent manganese, 0.40.85 percent silicon and a maximum carbon contentof 0.08 percent.

Proportions throughout the Specification are proportions by weight andthe mechanical properties of weld metal are those obtained by tests inaccordance with the mechanical test procedure of 8.8.5. 639, 1964.

Electrodes for carrying out the process according to the invention havea mild steel sheath, which may be formed from either rimming steel stripcontaining less than 0.12 percent carbon, O.20.6 percent manganese, lessthan 0.5 percent silicon, less than 0.04 percent sulfur and less than0.04 percent phosphorus, or from killed or semikilled strip with up to0.3 percent silicon, up to 0.15 percent carbon, up to 1.8 percentmanganese, less than 0.04 percent sulfur and less than 0.04 percentphosphorus.

The aluminum content of the electrode, which is present in the core, maybe metallic aluminum or ferroaluminium and the core will normallycontain both manganese and silicon, as such or as ferroalloys or presentas compounds, such as manganese oxide or silica, which will be reducedby aluminum to elementary form when the electrode is used for welding.The electrodes also contain in the core sufficient calcium fluoride, orofa balanced mixture of other fluorides of alkali or alkaline earthmetals to ensure regular bumoff of the tip of the electrode andsatisfactory spreading and wetting qualities of the slag and weld metalin order to ensure absence of significant porosity in the weld metal.

In general electrodes according to the invention may be manufactured bybending a mild steel strip, of width 0.6 inches and thickness 0.025,inches into a U-shaped channel measuring 0.2 across its mouth,introducing the core material into the channel, closing the channel anddrawing it down to a diameter between three sixty-fourths and one-eighthinch. In order to remove moisture and drawing soap the resulting tubeshould be baked in air at 250300 C for 30 to 60 minutes and it may thenbe coiled on spools. As an alternative, and if it is desired to reducethe springiness of the coils, the tube may instead be baked at 450 C inan atmosphere of nitrogen.

These electrodes fall into various categories, which will now bedescribed in detail.

Category 1 Electrodes of this category contain in the core metal powdersor wires in amounts such that the electrode as a whole contains 0.8-2.5percent aluminum 0.0ll percent titanium, 0.05l.5 percent silicon and0.4-l.5 percent manganese; 0.46 percent of fluorides of alkali oralkaline earth metals and slag forming materials. The aluminum siliconand manganese act as deoxidizers and, in addition, both the aluminum andsilicon reduce nitrogen absorption by the weld pool and fix freenitrogen as nitride. Although titanium increases the nitrogen solubilityin the weld pool, it also acts as a nitrogen fixing element and fixesthe nitrogen in the relatively harmless form of titanium carbonitridewhich does not form a dendritic structure. Concentrations of titanium inexcess of that just stated are deleterious to the impact properties andcould result in recovery into the weld metal of an amount of titaniumgreater than that specified above. The core generally amounts to 25-30percent by weight of the electrode.

While the electrodes of this category must contain at least 0.4 percentof fluorides of alkali and/or alkaline earth metals, which may bepresent as borofiuon'des, silicofluorides or titanofluorides, some ofthe fluoride content in excess of 0.4 percent may be replaced bycarbonates or titanates of alkali or alkaline earth metals. Theseingredients give a stable are, reducing spatter and loss of alloyingelements and improving the general ease of operation of the electrode.

Alumina derived by oxidation from aluminum in the core tends to give aninfusible and adherent slag and the slag formers in the core arematerials which are capable of forming with this alumina a slag of lowmelting point. Fluxes based on sodium oxide, and/or potassium oxidetogether with silica are capable of taking up alumina up to about 50percent of their weight while retaining a melting range of l300l500 C.Limited additions of lime and iron oxide help to retain a low meltingpoint. The fluxes may consist of potash felspar, which containsapproximately 14 percent K 62 percent SiO l percent Na and 18 percent A10 or of synthetic fused potassium silicate. Alternatively, soda felsparcontaining approximately 11 percent N 0, 68 SiO and 19 percent A1 0 orsodalime felspar or fused sodium silicate are suitable. They may be usedalone or as a mixture. The amounts of these materials, based on theweight of the electrode, are:

1. 4-8 percent potash felspar and/or soda felspar and/or lime felspar,or 48 percent of fused potassium silicate and/or sodium silicate.

2. 0-2 percent of calcium carbonate.

3. 5 percent of calcium metasilicate as natural or syntheticwollastonite.

4. 0-5 percent magnetic iron oxide or other iron oxide. The total amountof slag forming elements added is, in general, less than l0 percent.

Electrodes of this category yield weld metal of the following percentagecomposition:

ceptable slag. it is also highly desirable that the electrode 7 shouldinclude a small amount of ferrotitanium with a view to eliminating,entirely or almost entirely, porosity in the weld deposit. The fluoridecontent includes calcium fluoride or cryolite but may also containpotassium titanofluoride or sodium fluoride.

The following is the overall composition of the electrode in percentagesby weight:

Titanium as ferrotitanium 0.1 percent max. Overall Preferred l0Manganese 0.8-1.5 percent range range Potassium carbonate 0--0.2 percentg fi 8- 3 0 3-0- 5 Sodium or potassium silicate 00.3 percent nafitsati"6.3412 0. 5 1 3 Flourides, percent gigarriliumegg-g 0 0 at least 1.7percent of the fluoride content being calcium 1 p 111 Phosphorus. 10.035 0.01-0.02 15 fluondepr y l I on (apa t from incidental pu s)Balance Balance Titanium oxide as trtanates or minerals 0.25 percent 1Maximum.

Aluminum 1.2-2.6 percent Silicon, other than in silicates andferroalloys 0.03 per- 20 cent max.

The weld metal obtained has an ultimate tensile strength of 2836 tonsper square inch, an elongation of 21- 35 percent, a reduction of area of35-75 percent and a Charpy impact strength as specified above.

The following are examples of two typical electrodes of this category,the proportions being by weight of the electrode:

Aluminium 1. 75 1. 9 Manganese. 1. 30 1. Silicon 0. 0. 3 Titanium. 0. 25O. 15 Sulphun. 0. 03 0. 025 Phosphorus 0. 02 0. 02 K200 0. 1 NaF 0. 1 0.1 LiF 0. 25 0. 2 1412003 0. 1 0. 1 CsF. 0. 1 0. 1 KzTlFe O. 25 0. 35Potash feldspar 3. 0 4. 0 Soda feldspar 3. 0 2. 0 Magnetic iron oxide.0.6 0.3 08603 1. 0 l CaSiO 1.5 Iron Balance category 2 Electrodes ofthis category deposit weld metal of the following percentage compositionby weight:

The electrodes contain aluminum in the core, of which about half isrecovered in the weld metal the remainder being oxidized to aluminumoxide which forms a slag.

The aluminum oxide presents a problem in that it interferes seriouslywith the deposition of the weld metal, tending to form irregular slagglobules of high melting point which spoil the appearance of the weldand cause excessive undercut or sharp notches at the toes of the weld,which may seriously reduce the effective strength of a weldedfabrication. The surface tension of the molten metal is affected andweld ap- EXAMPLES OF CORE COMPOSITION IN PERCENT BY WEIGHT OF ELECTRODEExperimental No 403A 403 406 408 404 v Ferrotitanium (25 0. 25 0.30 0.300. 25 0.30 e, Ferrornanganese. 0. 73 0. 73 0.73 0.60 0. 70 0. b K2CO3.0.07 O. 07 0.14 0. 0. 07 0.17 Fused sodium 0.2 0.2 0. 0.26 Rutile sand0. 2 CaFz 3. 3 N agAlFg. Kz'IiF 0. 1 40 NaF 0.1 Aluminium (wire) 1. 75Iron powder (low 0) 13. 3

The above-noted constituents were contained in the core of theelectrode, of which the iron sheath represented 80 percent by weight andwas of the following composition 0.06 percent- C, 0.4 percent Mn, traceSi, 0.03 percent S, 0.02 percent P, balance Fe.

pearance deteriorates. A high spatter loss is associated with 70 minumoxide dissolves in the liquid fluoride to form an ac- 7 5 MECHANICALTEST RESULTS Experimental N 0 403A 403 406 408 404 411 YP, t.s.i. (tonsper square inch). 25. 12 25. 44 20.80 27. 04 20 20 27. 2 UTS, t.s.i 31.52 31. 36 29. 36 32. 80 28. 64 28 32. 6 Elongation, percen 24 24. 3 2723 26 26 25 Reduction of area 51 48 49 45 60 45 55 Charpy ft. lbs.:

At 20 54 43 74 76 52 50 At 0 C... 38 34 69 61 39 35 At -10 0.-.. 29 2658 43 28 34 At 30 C 24 20 46 37 22 29 1 Average of 3 specimens. 60

WELD METAL COMPOSITION IN PERCENTAGES BY WEIGHT Experimental N o 403A403 406 408 404 411 Manganese 1.0 1. 05 1.14 0.81 1.06 0.73 Silicon 0.25 0. 27 0.21 0.22 0. 22 0. 23 Titanium. 0. 20 0. 21 0. 13 0.20 0.230.17 Alumini 0. 73 0. 77 0. 805 0. 83 0. 77 O. 82 Iron (apart fromincidental impurities) 1 Balance.

Category 3 Electrodes of this category are based on the discovery thatthe good impact properties of the weld metal are retained, and 5 indeedimproved, and improved arc stabilization and easier slag removal areachieved when the core of electrodes of category 2 contains a chlorideof one or more of the metals caesium, potassium and sodium in an amountof 0.ll percent by weight of the electrode. Similar beneficial resultsare obtained by the inclusion in .the core of up to 1 percent by 5weight of the electrode of a carbonate of an alkaline earth metal or ofan alkali metal. The content of silicate of sodium or potassium in thecore may, moreover, be increased to 0.4 percent by weight of theelectrode.

The above-stated modifications tend to reduce the content of theincidental impurities sulfur and phosphorus in the weld metal to a valuewhich is normally below 0.016 percent in the case of each of theseelements, so improving the impact resistance of the weld metal.

The following are the compositions of some typical electrodes of thiscategory. In. each case the sheath of the electrode was of the mildsteel specified in category 2, and the core constituted 22 percent byweight of the electrode. The core constituents specifiedbelow are inpercentages by weight of the electrode.

Electrode 1 seas:

9 attest mm H wees;

NaCl 0.05 Fused sodium silicate (33% NaO)... 0.30 0.36 0.27 0.27 0.27Iron powder 1 Balance.

The following are the compositions of weld deposits produced by theseelectrodes:

Electrode 1 2 3 4 5 6 5 Carbon, percent 0.07 0.075 0. 109 0. 119 0. 1020.06 Manganese, percent 0.87 0.93 0. 90 0.90 0.90 1.04 Silicon (fromsilicate), percent. 0.21 0.24 0. 19 0.23 0. 18 0. 14 Titanium, percent0. 13 0.09 0.06 0.11 0. 11 0. 08 Aluminium, percent. 0. 74 0. 61 0. 620. 79 0. 84 1. 10 Sulphur, percent.. 0.013 0.011 0.018 0.018 0.015 0.02Phosphorus, percent. 0. 014 0.012 0. 015 0. 015 0.015 0. 012 on 4 Thefollowing are the mechanical properties of weld metal deposited byElectrodes 3-6:

Category 4 The electrodes of this category are of the followingcomposition in parts by weight of the electrode:

Overall range Preferred range Carbon 0.3% maximum... 0.2% maximum.Aluminium... to 3 Manganese... Silicon.... Fluorides Overall rangePreferred range Carbonates 1 to 6% 2.5 to 3.5%. Slag balancers 0 to 4%0.2 to 1.0%. Iron (apart from 1 impurities) Balance Balance The ratio byweight of fluorides to carbonates is 3.2-6 and preferably 4.24.7. Thealuminum may be present in the core as metallic powder, ferroalloy or aswire.

Manganese is derived partly from the sheath and partly fromferromanganese or silicomanganese in the core. Ferromanganese typicallycontains percent manganese and 0.5 percent carbon with balancesubstantially iron but a carbon level of 6 percent is acceptable.silicomanganese typically contains 60 percent silicon and 40 percentmanganese.

Silicon is derived chiefly from the core being present, for example, asa ferroalloy or as silicomanganese but a small amount, for example 0.02percent of silicon may be present in the sheath.

The fluoride content of the electrode is such that the electrodecontains at least 8 percent of calcium fluoride. When, however, theamount of calcium fluoride substantially exceeds this FIG. part can bereplaced by cryolite. The carbonates are selected from barium,calcium,-strontium or magnesium carbonate, but potassium carbonate maybe used in an amount of up to 2 percent by weight of the total contentof carbonates.

The slag balancers, which control the fluidity of the slag by stiffeningit, are selected from alumina, silica, titania and zirconia and may bepresent as these oxides or as compounds of these oxides such aspotassium titanate, sodium silicate or felspar. A small quantity of slagbalancer may be helpful in giving exactly the degree of slag followupnecessary. We prefer to use alumina but the other slag balancers areadequate but must not be used in sufficient quantity to give asignificant alloying recovery into the weld metal due to reduction byaluminum To ensure that the titanium content of the weld metal does notexceed the above-stated amount and that zirconium is not present in theweld metal otherwise than as an incidental impurity, the amount oftitania and/or zirconia should not exceed 0.5 percent by weight of theelectrode.

Iron is derived from the sheath, ferroalloys and iron powder in thecore. There is no objection to the use of iron powder containingsignificant amounts .of carbon providing the amount of carbon does notexceed the above stated maximum. This is to ensure that carbon recoveryinto the weld metal does not exceed the limit stated below.

The electrodes of this category are intended primarily for welding inthe horizontal and flat positions and give weld deposits of good shapewith fine ripple marking, a good washout at the toes of the weld andweld metal of high ductility and good impact strength. The electrodesare easy to use, require no special degree of concentration on the partof the operator and hence reduce operating fatigue. The deposition rateof weld metal from the electrodes is high and hence the electrodeassists in rapid welding and fabrication. The slag followup is good andthe weld pool is easily observable.

The electrodes may contain iron powder in an amount of up to 35 percentby weight of the electrode. When iron powder is present in the core, thecore should constitute at least 20 percent by weight of the electrode inorder to ensure a fast deposition rate and the core may amount to asmuch as 48 percent by weight of the electrode. The range of 2435 percentby weight of core to electrode is preferred. When the core contains noiron powder it is, of course, lighter and in this case the ratio byweight of core to electrode may be l420 percent and is preferably 16-18percent.

The weld metal deposited by electrodes of this category is as follows;

Overall Preferred range range Carbon, percent.. 0. 13 0.11 Aluminium,percent... 0. 25-1. 0. 45-0. 8 Manganese, percent- 0.4-1. 8 0.6-1. 2Silicon, percent. 1 0. 0.2-0. 4 Titanium, percent. l 0. 12 1 0. 1Sulphur, percent l 0.03 1 0.02 Phosphorus, percent.. 1 0.03 l 0. 02 IronBalance Balance 1 Maximum.

Aluminium powder 8 9 8 8 9 10 9 6 16 Ferromanganese. 3 2 3 3 3 3 3 2 5Ferrosilicon-.. 2 1 2 2 1. 5 1. 5 1 2. 5 3

1 0. 5 $4 .is" l 1 1 2 Iron powder 583-7333;; 24 455""5164"as-iii:

Calcium carbonate 6 4 6 3 3 4 4 3% 12 Magnesium carbonate. 2 7 5 9 4 1.5 2 Core as percentage by weight of the electrode. 28 25 25 25 32 33 3643 Mechanical Test Results from Example No. 1.

Yield point t.s.i. 26.2 U.T.S. t.s.i. 33.7 Elongation percent 21 R. ofA. percent 47 Charpy ft. lbs. at C 45 (average of three specimens)Category 5 These electrodes include in some instances manganese oxide inthe core and sufficient aluminum to reduce the oxide to manganese whichis recovered, as such, in the weld metal. The core constitutes 33percent by weight of the electrode and the core is of the followingcomposition by weight:

General Preferred range range Iron powder, percent 0-40 5-30 Aluminiumpowder, percent. 4-20 8-15 Maganese oxide, percent 0-15 3-10 Iron oxide,percent 0-25 2-15 Silica, percent 0-15 3-10 Potassium titanate and/orrutile, percent. 0-10 1-7 carbonates, percent 0-10 2-8 Fluorides,percent 10-40 15-30 potassium silicofluoride, sodium fluoride and/orpotassium fluoride.

The following are examples of core compositions of typical electrodes ofthis category:

Iron powder 30 30 30 22 30 Aluminum powder 12 12 12 13 12 The weld metalcompositions obtained with these electrodes were as follows:

Titanium, percent 0. 05 0. 05 0. 05 0. 06 0. 06 Aluminum, percent 0. 400.30 0.41 0.41 0. 47 Manganese,perceut.. 1.35 0.70 1.85 1.31 1.34Silicon,percent 0.51 0.70 0.28 0.45 0.53 Carbon, percent 0.06 0.08 0.050.06 0.06

Iran the balance, apart from incidental impurities.

lron the balance, apart from incidental impurities. The mechanicalproperties of weld metal obtained from these electrodes were as follows:

1 Average of 3 specimens.

Certain further electrodes according to the invention and the conditionsto be observed during use of these electrodes will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a transformer circuit, and

FIGS. 2 and 3 are graphs illustrating conditions of electrode operationwith DC and AC welding current respectively.

When electrodes according to the invention are to be used with ACcurrent at a current density of 20,000l00,000 amperes per sq. in., theyshould have a diameter in the range of 0.03-0. 14 inch and be of thefollowing composition in parts by weight of the electrode:

Overall range Preferred range Aluminium. 1.5 to 4.5%

0.5 to 1%: 0.25% maximum.

Calcium fluoride Arc stabilisers 2 to 3.5%. Slag modifiers 1 to 4% Ironand incidental impuriti Balance While the fluoride constituent isspecified as calcium fluoride it may contain minor amounts of otherfluorides such as sodium fluoride or cryolite.

The arc stabilizers in the above table are oxides of magnesium, alkalimetals or alkaline earth metals, which may be present as such or ascompounds, such as carbonates, titanates or silicates, which willdecompose to yield these oxides at the temperature of the arc. Theamount of fluoride plus arc stabilizers must amount to at least 5.5percent by weight of the electrode. The slag modifiers in the abovetable are alumina, silica, titania and/or zirconia, as such or ascompounds which will decompose to yield these oxides, with the provisothat the amount of titania and/or zirconia must not exceed 0.5 percentby weight of the electrode.

Calcium and magnesium carbonates are effective are stabilizers. butsuitable alternatives are carbonates of strontium, barium, lithium,caesium, rubidium, sodium and potassium.

(32100 percent. MgCO percent K2003, percent Iron as sheath.

1 Balance.

As will be apparent from the foregoing, the electrodes to be used inaccordance with the invention consist of a mild steel sheath enclosing acore containing nitrogen fixing and deoxidizing elements and cansuccessfully be used without shield- Iron powder in the core of theelectrode assists in arc stabiliza- 5 ing because these elements remove,or at least nullify, the tion and should preferably be present in anamount of not less harmful effects of atmospheric it o nd o yg hi h than6 percent by weight of the electrode. There is no objecenter the weldpool and which, but for the effect of deoxtion to the use of grades ofiron powder containing up to 0.3 idiiers and nitrogen fixers, wouldcause a very severe loss of percent by weight of carbon. As alreadynoted, are stabilizing impact strength and ductility. It is essential,in order to secure elements may be present as carbonates or oxides orother 10 weld metal as specified above, that some amounts ofalucompounds which willyield oxides at are temperatures. minum manganeseand silicon are recovered into the weld The above-described slagmodifiers may be replaced by an metal but the extent of recovery variesaccording to the foloxide of manganese and/or iron, which also tends tostabilize lowing fa t rs the arc, but in this case the electrode willcontain more alu- Th arc length has a major effect On alloy recovery, 3minum to ensure oxidation to metal of said oxide and the long arctending to lose by atmospheric reaction much of the preferred range ofaluminum content will be 2.5-4.5 percent. alloying l m n present in theelectrode and a short are In this case the content of manganese oxidemust not exceed 3 assisting their r v ry.

per ent b t th tent of ir id may b as hi h as 5 2. The welding currentalso has a major effect on recovery, cent. a high current increasingrecovery and a low current diminish- Electrodes as just describeddeposit ductile, tough weld ing recovery. metal containing 0.4l.6percent manganese, 0.2-1 percent Accordingly, if the arc length isexcessive too much alualuminum, 0.5 percent max. silicon, 0.15 percentmax. titanimi um Will be l st and the Weld metal is liable to become umirconium, balance iron apart from incidental impuripOl'OUS, while if thearc length is 1100 ShOlt and the welding CU!- ties. Preferably the weldmetal is of the following composition: rent is too high, so muchaluminum, and p p also silicon carbon 1 percent max aluminum percentman. and manganese, be retained in the weld metal SO 35 to inganese 6 .11 percent, ili 0 2 4 percent, i i Q. crease its tensile strength andundesirably reduce its ductility. 1 percent, lf 103 percent maxphosphorus 003 It IS accordingly highly desirable to operate theelectrodes cent max. iron the balance under conditions such thatV=1.9A+x when AC welding cur- The AC power source may be of anyconventional type and rent i used and V=l-1A\ll DC welding CuTTFm isUsed? good results may be obtained by the use of conventional trans- Vbeing the are g A being the current density expressed formers primarilydesigned for welding with manual elecas trodes. Thus the power may bederived from the mains 1 6 through a transformer or may be provided by asuitable AC 1-066 3 generator. It may be single phase, three phase orderived from two phases of between line and n r l f a hr Phase where cis the welding current in amperes andd is the diamesupply. The loadcharacteristic of the transformer may be of ter of the ele trode ininches, X being between 18 and 29 and the drooping, sloping or leveltype. t; being between 19 and 30.

A typical transf rm r circuit is Sh wn in FIG. 1 0f t Operation thustakes place in the regions between the .lines drawings, in which L Lrepresent the AC supply terminals, T A and B in FIG. 2 and between thelines C and D in FIG. 3 of represents a transformer, I represents aninductance and T,, the drawings, in which arc voltage is plotted asordinates and T are terminals for connection to the work and to theeleccurrent density as abscissae. These lines are as follows: troderespectively. Line A V=l .9A+29 In a conventional circuit for manual arcwelding, using a LineB V=l.9A+l8 250 volt AC supply, the transformer Tis designed to give .an LineC V=l. 1A+30 open circuit voltage of 80volts and the inductance I has a Line D V=l.lA+l9 value of 0.5millihenries. For use in accordance with the If OPCIfltiOH t es Place{lbove line A C the Weld present invention the transformer may bedesigned to give an metal tend? to exhibit p y While If P Place Opencircuit voltage f 30. 0 volts d the i i so below the line B or D theweld metal tends to exhibit a loss of ranged as to cause the voltage todrop to 25-40 volts when ductility and Impact Strength the arc is struckand the characteristic to be substantially sansfactoliy weld can beSecured y Compliance i level, the voltage drop being within the range of0-0.1 volts m P conditions 115mg 3 Pl electrode having per ampere andpreferably volts per ampem within its mild steel sheath a corecontaining 0.8-4.5 percent The following are examples of typicalelectrodes for use alummum 00'6 percent Percen} mamum under theabovedescribed AC Current conditions: and 0.3l.6 percent manganese basedon the weight of the In each case the diameter of the electrode is0.094, the electrode h h ff f sheath is of rimming quality mild steelcontaining 0.06 percent i the l p i gg t C, 0.5 percent Mn, 0.03 percentS, 0.03 percent P, balance workmg f i PP Y on 6 iron; the coreconstitutes 30 percent by weight of the elecelect) em] 16 as m Categorya trode and the composition is as follows in percentage by weight of theelectrode. Test 1 Test 2 Test 3 Are, volts 21 26 35 1 2 3 4 5 Weldingcurrent, amps 400 400 400 Current density, as defined above 4. 3 4. 3 4.3

Aluminium powder, percent... 2. 2 2. 4 4. 4 3.8 3. 3 Al in weld 1. 3 0.70. 3

Manganese, percent 0. 7 0.8 Si in weld 0. 5 0. 25 0. l2

M11203, percent 1. 4 0.95 0.7 Ferrosilicon, percent Ultimate tensilestrength of weld metal,

Calcium fluoride, percent t.s.i 39 33 24 Alumina, percent Elongation,percent 16 24 10 Silica, percent 0. Reduction of area, percent 31 47 15Iron powder, percent 11 7 8 9 7 Charpy Impact Strength at 0 0.... 18 6 3Fe oi, percent 5 Weld metal soundness Good Good Porous We claim: 1. Aprocess of automatic or semiautomatic welding which consists in arcdepositing from a cored tubular electrode, having a mild steel sheathdevoid of external flux, without external shielding of the arc, weldmetal having an elongation of at least 18 percent, a reduction of areaof at least 25 percent, and a Charpy impact strength of at least 35ft/lbs, at 20 C and at least 20 ft/lbs. at 30 C when tested inaccordance with the mechanical test procedure given in 8.8.8. 639, 1964,the weld electrode includes the following materials in such quantitiessuch that weld metal is of the following composition by weight:

aluminum 0.l2-l .3 percent manganese 0.3-2 percent silicon 0.1-1 percentcarbon 0.12 percent max. titanium 0.12 percent max. if the siliconcontent exceeds 0.35 percent and 0.25 percent max. if the siliconcontent is 0.35 percent or less balance iron apart from incidentalimpurities. 2. A process as claimed in claim 1, in which the weld metalcontains 0.12-0.8 percent aluminum, 0.7l.75 percent manganese, 0.40.85percent silicon and a maximum carbon content of 0.08 percent.

3. A process as claimed in claim 1, in which the electrode is used withAC current at a current density of 20,000120,000 amperes per sq.in.

4. A process as claimed in claim 3, in which the power supply yields anopen current voltage of 30-60 volts and a voltage drop not exceeding 0.1volts per ampere.

5. A process as claimed in claim 1, in which the welding operation iscarried out under conditions such that V=1.9A+x when AC welding currentis used and V=l.lA+1l1 when DC welding current is used; V being the arcvoltage, A being the current density as hereinbefore defined, beingbetween 18 and 29 and 111 being between 19 and 30.

6. A process as claimed in claim 5, in which the core of the electrodecontains 0.84.5 percent aluminum, 0-0.6 percent silicon, O0.3 percenttitanium and 03-16 percent manganese based on the weight of theelectrode.

2. A process as claimed in claim 1, in which the weld metal contains0.12-0.8 percent aluminum, 0.7-1.75 percent manganese, 0.4-0.85 percentsilicon and a maximum carbon content of 0.08 percent.
 3. A process asclaimed in claim 1, in which the electrode is used with AC current at acurrent density of 20,000-120,000 amperes per sq.in.
 4. A process asclaimed in claim 3, in which the power supply yields an open currentvoltage of 30-60 volts and a voltage drop not exceeding 0.1 volts perampere.
 5. A process as claimed in claim 1, in which the weldingoperation is carried out under conditions such that V 1.9A+ Chi when ACwelding current is used and V 1.1A+ psi when DC welding current is used;V being the arc voltage, A being the current density as hereinbeforedefined, Chi being between 18 and 29 and psi being between 19 and
 30. 6.A process as claimed in claim 5, in which the core of the electrodecontains 0.8-4.5 percent aluminum, 0-0.6 percent silicon, 0-0.3 percenttitanium and 0.3-1.6 percent manganese based on the weight of theelectrode.